Ablation catheter tip with flexible electronic circuitry

ABSTRACT

Aspects of the present disclosure are directed to, for example, a high-thermal-sensitivity ablation catheter tip including a thermally-insulative ablation tip insert supporting at least one temperature sensor electrically coupled to a flexible electronic circuit and encapsulated, or essentially encapsulated, by a conductive shell. Also disclosed is a method of controlling the temperature of an ablation catheter tip while creating a desired lesion using various forms of energy and energy delivery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.62/517,594, filed 9 Jun. 2017, and which is hereby incorporated byreference as though fully set forth herein.

This application claims the benefit of U.S. provisional application Nos.62/404,060, 62/404,038, and 62/404,013, all of which were filed 4 Oct.2016, which are hereby incorporated by reference as though fully setforth herein.

This application incorporates by reference as though fully set forthherein, U.S. application Ser. No. 15/088,036, filed 31 Mar. 2016, nowpending, which claims the benefit of U.S. provisional application No.62/141,066, filed 31 Mar. 2015; U.S. application Ser. No. 15/088,052,filed 31 Mar. 2016, now pending, which claims the benefit of U.S.provisional application No. 62/198,114, filed 28 Jul. 2015.

BACKGROUND OF THE DISCLOSURE a. Field

The present disclosure relates to low thermal mass ablation cathetertips (also known as high-thermal-sensitivity catheter tips) and tosystems for controlling the delivery of RF energy to such cathetersduring ablation procedures.

b. Background

RF generators used during catheter ablation procedures are often set ina “temperature control” mode, and the power is initially set to a valuethat is sufficiently high (for example, 35 Watts) to create lesions intissue and the tip temperature is set to, for example, 40° C. As soon asthe tip reaches 40° C., the power is titrated down to a lower powersetting such as, for example, 15 Watts to maintain the 40° C. targettemperature. This can, however, create problems in that such lower powersettings (e.g., 15 Watts) may be too low to create lesions that are deepenough to be effective for treating abnormal heart rhythms.

The foregoing discussion is intended only to illustrate the presentfield and should not be taken as a disavowal of claim scope.

BRIEF SUMMARY OF THE DISCLOSURE

It is desirable to be able to control the delivery of RF energy to acatheter to enable the creation of lesions in tissue by keeping thegenerator power setting sufficiently high to form adequate lesions whilemitigating against overheating of tissue. Accordingly, aspects of thepresent disclosure are directed toward an ablation catheter tipincluding high thermal sensitivity materials which facilitate nearreal-time temperature sensing at the ablation catheter tip.

Aspects of the present disclosure are directed to ahigh-thermal-sensitivity ablation catheter tip. The tip including anelectrically-conductive housing, a thermally-insulative tip insert, anda flexible electronic circuit. The electrically-conductive housingcomprising a conductive shell that surrounds at least a portion of thetip insert. The flexible electronic circuit is circumferentiallydistributed around the tip insert, and includes a plurality of thermalsensors, and a wired or wireless communication pathway. The plurality ofthermal sensors are in thermal communication with the conductive shelland provide directional temperature feedback. The plurality of thermalsensors are distributed across at least one of a length and width of theflexible electronic circuit. The wired or wireless communicationpathway, at least partially disposed on the flexible electronic circuit,is communicatively connected to the plurality of thermal sensors, andreports the directional temperature feedback to an ablation controlsystem.

Some embodiments of the present disclosure are directed to an ablationtip for an ablation catheter. The ablation tip including a thermally andelectrically conductive housing, a thermally-insulative tip insert, anda flexible electronic circuit. The thermally and electrically conductivehousing includes a conductive shell that includes an inner surface, andsurrounds at least a portion of the tip insert. The flexible electroniccircuit is circumferentially mounted around the tip insert and islocated between the conductive shell and the thermally-insulative tipinsert. The flexible electronic circuit includes at least three thermalsensors, and a wired or wireless communication pathway. The thermalsensors are placed in thermally-transmissive contact with the innersurface of the conductive shell, and receive and report temperaturefeedback received via the conductive shell. The wired or wirelesscommunication pathway is communicatively connected to the thermalsensors, and facilitate reporting of the temperature feedback to anablation control system.

Further embodiments are directed to an ablation catheter tip havinghigh-thermal-sensitivity. The tip including a thermally-insulativeablation tip insert, a conductive shell, and a shank. Thethermally-insulative ablation tip insert includes a first portion and asecond portion, and is adapted to support at least one flexibleelectronic circuit including a plurality of temperature sensors. Theconductive shell is configured to fit around the first portion of theinsert in thermally-conductive contact with the plurality of temperaturesensors, while the shank covers the second portion of the insert. Theconductive shell and the shank are conductively coupled and togethereffectively encase the ablation tip insert.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS

Various example embodiments may be more completely understood inconsideration of the following detailed description in connection withthe accompanying drawings, in which:

FIG. 1 is a highly-schematic representation of one embodiment of asystem for delivering pulsed RF energy during catheter ablation, showingpossible communication pathways between primary components in thisembodiment.

FIG. 2 is similar to FIG. 1, but depicts the components arranged in aslightly different configuration in an alternative embodiment of asystem for delivering pulsed RF energy during catheter ablation.

FIG. 3 is similar to FIGS. 1 and 2, but depicts a system with adedicated central processing unit interfacing with the components alsodepicted in FIGS. 1 and 2.

FIG. 4 schematically depicts a catheter in use in a patient andconnected to a generator comprising a pulsed RF control system accordingto the present disclosure.

FIG. 5 depicts one possible control flowchart, including variousoptional steps, for delivering pulsed RF energy to an ablation catheter.

FIG. 6 depicts six representative controller responses, showing how ameasured process variable may approach a set point depending on how thecontroller is configured.

FIG. 7 depicts a representative controller response and depicts how ameasured process variable (PV) at a first set point (“initial steadystate value of PV”) may be driven to a second set point (“final steadystate value of PV”).

FIG. 8 is a fragmentary, isometric view of various components comprisingthe distal end of an ablation catheter that could be used with thepulsed RF control systems disclosed herein.

FIG. 9 is similar to FIG. 8, but depicts components of the distal end ofa non-irrigated catheter that could be used in combination with thepulsed RF control systems disclosed herein.

FIG. 10 is an exploded, isometric view of the catheter tip depicted inFIG. 8, showing additional components and features.

FIG. 11 is a side view of the conductive shell depicted in, for example,FIGS. 8 and 10.

FIG. 12 is an isometric view of the conductive shell depicted, forexample, in FIGS. 10 and 11.

FIG. 13 is a cross-sectional view showing the interior of the conductiveshell depicted in, for example, FIGS. 10-12.

FIG. 14 is an enlarged isometric view of the shank also depicted in, forexample, FIGS. 8-10.

FIG. 15 is an isometric, cross-sectional view of the various cathetertip components also depicted in FIG. 8.

FIG. 16 is similar to FIG. 15, but is a cross-sectional view taken at anangular orientation that bisects two of the lateral irrigation channels.

FIG. 17 is an enlarged, fragmentary, cross-sectional view showing apossible interconnection between the shell cylindrical body, the shank,and an RF lead wire.

FIG. 18 is a fragmentary, isometric, cross-sectional view of a priorart, solid platinum (or solid platinum iridium) irrigated catheter tipwith a polymer irrigation tube mounted in its proximal end.

FIG. 19 is similar to FIGS. 15 and 16, and depicts another fragmentary,isometric, cross-sectional view, but this time taken from an angularorientation that clearly shows a distal-most thermal sensor.

FIG. 20 is an isometric view of components of the tip also depicted in,for example, FIGS. 8, 10, 15, 16, and 19.

FIG. 21 is similar to FIG. 20, but shows the catheter tip components ina different orientation, revealing the distal-most thermal sensor; andthis view also includes the shank, which is not present in FIG. 20.

FIG. 22 is an isometric view of the thermally-insulative ablation tipinsert also depicted in FIG. 21.

FIG. 23 depicts the tip insert of FIG. 22 in a slightly differentangular orientation, revealing an arc-shaped channel or ditch thatextends toward the distal end of the catheter tip to position thedistal-most thermal sensor at that location.

FIG. 24 depicts a thermally-insulative ablation tip insert for anon-irrigated embodiment of a catheter tip, such as the embodimentdepicted in FIG. 9.

FIG. 25 is most similar to FIG. 8, but depicts an alternative embodimentcomprising one or more isolated temperature-sensing islands.

FIG. 26 is most similar to FIG. 12, but depicts a multilayer embodimentof the conductive shell.

FIG. 27A schematically depicts magnetic flux lines reacting to adiamagnetic sub stance.

FIG. 27B schematically depicts magnetic flux lines reacting to aparamagnetic sub stance.

FIG. 27C schematically depicts magnetic flux lines reacting to aferromagnetic sub stance.

FIG. 28 is most similar to FIG. 20, but depicts an embodiment of the tipinsert on which both distal and proximal temperature sensors aremounted.

FIG. 29A is a top view of a multi-layer flexible circuit includingthermocouples and spot electrodes, consistent with various aspects ofthe present disclosure.

FIG. 29B is a top view of a top copper layer of the multi-layer flexiblecircuit of FIG. 29A, consistent with various aspects of the presentdisclosure.

FIG. 29C is a top view of a bottom constantan layer of the multi-layerflexible circuit of FIG. 29A, consistent with various aspects of thepresent disclosure.

FIG. 30 depicts an isometric view of a tip insert, consistent withvarious aspects of the present disclosure.

FIG. 31 depicts an isometric front view of a partial catheter tipassembly including a tip insert, as shown in FIG. 30, with a multi-layerflexible circuit, as shown in FIGS. 29A-C, wrapped circumferentiallyaround the ablation tip insert, consistent with various aspects of thepresent disclosure.

FIG. 32 depicts an isometric front view, including a partial cut-out, ofthe partial catheter tip assembly of FIG. 31 with a conductive shellencompassing at least a portion of the tip insert and the multi-layerflexible circuit, consistent with various aspects of the presentdisclosure.

FIG. 33 depicts a top view of an embodiment of a multi-layer flexiblecircuit, consistent with various aspects of the present disclosure.

FIG. 34 depicts a top view of another embodiment of a multi-layerflexible circuit, consistent with various aspects of the presentdisclosure.

FIG. 35 depicts a top view of yet another embodiment of a multi-layerflexible circuit, consistent with various aspects of the presentdisclosure.

While various embodiments discussed herein are amenable to modificationsand alternative forms, aspects thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the invention tothe particular embodiments described. On the contrary, the intention isto cover all modifications, equivalents, and alternatives falling withinthe scope of the disclosure including aspects defined in the claims. Inaddition, the term “example” as used throughout this application is onlyby way of illustration, and not limitation.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a highly-schematic representation of one embodiment of asystem 10 for delivering pulsed RF energy to an ablation catheter 12during catheter ablation, showing possible communication pathways 14,16, 18 between primary components in this embodiment. This figuredepicts a generator 20 operatively connected to a pulse control box 22,which is operatively connected to the ablation catheter 12. In thisfigure, a number of possible wired and/or wireless communicationpathways are shown. For example, a dashed line 14 represents temperaturefeedback from the catheter to the pulse control box 22 of readings fromat least one temperature sensor mounted in the tip of the catheter 12.In this embodiment, and in all of the embodiments described herein, thecatheter may comprise multiple thermal sensors (for example,thermocouples or thermistors), as described further below. If thecatheter comprises multiple temperature sensors mounted in its tipregion, the feedback shown in FIG. 1 from the catheter to the pulsecontrol box may be, for example, the highest reading from among all ofthe individual temperature sensor readings, or it may be, for example,an average of all of the individual readings from all of the temperaturesensors.

In FIG. 1, two communication options, represented by double-headed arrow24 and single-headed arrow 26, are shown for delivering information tothe generator 20 or exchanging information between the pulse control box22 and the generator 20. The communication pathway 18 between thegenerator 20 and the pulse control box 22 could comprise, for example,multiple, separate electrical connection (not separately shown) betweenthe generator 20 and the pulse control box 22. One of thesecommunication lines could be, for example, a separate (possiblydedicated) line for communicating to the generator the highesttemperature measured by any of a plurality of temperature sensorsmounted in the catheter tip. This could be used to trigger atemperature-based shutdown feature in the generator for patient safety.In other words, the temperature reading or readings from the cathetermay be sent to the pulse control box, which may then feed the highesttemperature reading to the generator so that the generator can engageits safety features and shut down if the temperature reading appears tobe getting undesirably or unsafely high.

In an alternative configuration, the generator 20 “thinks” it isdelivering RF energy to the catheter, but that energy is being deliveredinstead to the pulse control box 22. The pulse control box thendetermines, based upon the temperature feedback that it receives fromthe catheter, whether to drive the catheter at the power level comingfrom the generator or, alternatively, to pulse the delivery of RF energyto the catheter tip. In this configuration, the generator may be blindto the fact that the pulse control box 22 is determining whether to sendpower to the catheter tip or to momentarily suspend delivery of energyto the catheter tip as a means of effectively controlling tissuetemperature by monitoring and controlling catheter tip temperature.

FIG. 2 is similar to FIG. 1, but depicts the components arranged in aslightly different configuration in an alternative embodiment of asystem 10′ for delivering pulsed RF energy during catheter ablation. InFIG. 2, the pulse control box 22 is again receiving temperature feedbackfrom the catheter 12 along communication pathway 14. However, in FIG. 2,the pulse control box 22 is “telling” the generator (e.g., alongcommunication pathway 18′) to switch “off” and “on” based on the sensedtemperature from the catheter 12. The generator 20 then delivers pulsedRF energy to the catheter 12 via communication pathway 28. In thissystem 10′ for delivering pulsed RF energy, as in the system 10 depictedin FIG. 1 and discussed herein, the power can remain at a desired powerlevel (e.g., 50 or 60 Watts) rather than being reduced to an ineffectivelevel when excessive temperature is sensed by the catheter tip. Inparticular, rather than reducing the power to control temperature, thepower is delivered in a pulsed manner; and it is the control of theenergy pulses, including control of the length of the time gaps betweenpulses, that is used to control the tip temperature as a surrogate forcontrolling the tissue temperature. As a further alternative for how thesystem 10′ depicted in FIG. 2 may operate, the generator 20 may receivetemperature feedback via communication pathway 28 and then passtemperature feedback information to the pulse control box 22, whichwould then control the generator 20 as described above.

FIG. 3 is similar to FIGS. 1 and 2, but depicts a system 10″ with adedicated central processing unit (CPU) 30 interfacing with thecomponents 12, 20, 22 also depicted in FIGS. 1 and 2. As shown in thisfigure, a dedicated CPU is among the components in the system 10″ fordelivering pulsed RF energy during ablation. This figure also shows anumber of potential communication pathways between and among the variouscomponents, including, for example, a temperature feedback pathway 32between the catheter and the CPU, the temperature feedback pathway 14between the catheter and the pulse control box 22, a communicationpathway 34 between the generator 20 and the CPU 30, a communicationpathway 18″ between the generator and the pulse control box, thecommunication pathway 28 between the generator 20 and the catheter 12,and a communication pathway 36 between the CPU and the pulse controlbox. The following are various possible combinations of pathways thatcould be used, assuming the overall system comprises at least the fourcomponents 12, 20, 22, 30 shown in this figure:

-   -   A. 14, 18″, 28, 32, 34, 36 (all)    -   B. 14, 28, 34, 36    -   C. 14, 34, 36    -   D. 14, 18″, 36    -   E. 32, 34, 36    -   F. 18″, 32, 36    -   G. 18″, 32, 34    -   H. 14, 18″, 34

As represented by the first set (i.e., set “A” above) of examplepathways noted above, all six communication pathways 14, 18″, 28, 32,34, 36 depicted in FIG. 3 could be used in a system for deliveringpulsed RF energy during a catheter ablation procedure. Alternatively,and as merely one more example, communication pathways 14, 28, 34, and36 may be the only four communication pathways required in the controlsystem. This is the second example listed above (i.e., set “B”). In eachof these communication pathway examples, it is assumed that thegenerator 20 is always connected to the catheter 12 in some way (asrepresented in FIG. 3 by the solid line 28 extending between thegenerator and the catheter). Thus, in yet another example operatingscenario, the generator 20 may directly receive temperature feedbackfrom the catheter 12 along, for example, communication pathway 28. Thegenerator 20 could then share that temperature feedback information withthe dedicated CPU 30 and/or the pulse control box 22 via one or more ofthe communication pathways 18″, 34, 36. Yet another possible alternativeto the system 10″ depicted in FIG. 3 would be to switch the locations ofthe pulse control box 22 and the generator 20, similar to theconfiguration depicted in FIG. 1, but also include the dedicated CPU 30depicted in FIG. 3. In this latter optional configuration, there may bea communication pathway (not shown) directly connecting the pulsecontrol box 22 to the catheter 12 (similar to communication pathway 16in FIG. 1).

FIG. 4 schematically depicts a catheter 12 in use in a patient 38 andconnected to a generator 40 comprising a pulsed RF control systemaccording to the present disclosure. This figure depicts a portion of ahuman torso of the patient 38, a heart, a representative catheter tiplocated in the heart, a representative catheter handle, and the RFgenerator. As shown in this figure, the catheter is assumed to beconnected to the RF generator 40. In this configuration, the pulsecontrol hardware, software, and/or firmware is built into the generatoritself

FIG. 5 is a flowchart depicting one possible control flow, includingvarious optional steps, for delivering pulsed RF energy to an ablationcatheter. In this representative, and not limiting, example of controlflow, the process commences at block 502. At block 504, the generator isplaced in a “power-control” mode. Next, at block 506 the generator poweris set to a desired power level for a desired initial time. In thisrepresentative flowchart, that initial power level is shown as 50 Wattsand the initial time is shown as 60 seconds; however, both of these aremerely sample values. If, for example, a physician is ablating a portionof the heart that lies near the esophagus, then the physician may chooseto use a lower power setting (e.g., 15 Watts) since the physician maydesire to create a relatively shallow lesion (e.g., a 1 mm deep lesion).At block 508, the pulse control may be set to set point 1. If, forexample, the pulse control box 22 (see, for example, FIG. 1) is a PIDcontroller (also known as a proportional-integral-derivative controlleror a three-term controller), set point 1 may relate to the measuredprocess variable (PV). That measured process variable may be thetemperature feedback coming from the catheter tip during the ablationcycle. As may be understood by one of skill in the relevant art, a PIDcontroller calculates an error value as the difference between ameasured process variable—e.g., measured tip temperature—and a desiredset point—e.g., a desired tip temperature. The controller then attemptsto minimize the error by adjusting the process through use of amanipulated variable (MV)—e.g., the time that a selected power isactively delivered to an ablation tip. The three parameters in a PIDcontroller are as follows:

1. the proportional value (P)—depends on present error;

2. the integral value (I)—accumulation of past errors; and

3. the derivative value (D)—predictive of future errors based on currentrate of change.

In an effort to achieve a gradual convergence to the set point, which,as discussed herein, may be desired catheter tip temperature, thecontroller calculates a weighted sum of P, I, and D, and then uses thatvalue to adjust the process—here by adjusting the time when RF power isdelivered to the ablation tip (e.g., by pulsing the delivery of RFenergy to the tip). In one embodiment of the system described herein, auser is allowed to “tune” the three values, namely the P, I, and Dvalues. The controller may be a separate controller as discussed hereinand shown in FIGS. 1-3 (e.g., pulse control box 22 in these figures), ormay be implemented as a microcontroller or a programmable logiccontroller (PLC) or in other firmware or software, all of which may be,for example, built directly into the generator 40 as shown in, forexample, FIG. 4. In the control systems described herein, RF power isturned “on” and “off” based on the temperature feedback as it isinterpreted and analyzed by the pulse control box. In block 510, theablation cycle begins.

In block 512, the control system monitors the catheter tip temperature.As noted above, this would be the “PV” value in a PID controller. Asrepresented by block 514 and its loop back to block 512, as long as thetip temperature is not close to set point 1, the system continues topermit the delivery of full RF power to the ablation tip and continuesto monitor catheter tip temperature at block 512. Once the measured tiptemperature is approximately at the value of set point 1 (e.g., 40° C.in one example), the pulse control box (e.g., the PID controller) wouldbegin to pulse the RF energy being delivered to the catheter tip (seeblock 516) in an effort to keep the tip temperature approximately at setpoint 1.

Continuing to refer to the flowchart in FIG. 5, at block 518, thetemperature setting on the pulse control box 22 is changed to set point2, which may be, for example, a higher value than set point 1. As shownin FIG. 5, in this example set point 2 is 55° C. At this point in theprocess, and in order to increase the tip temperature from set point 1to set point 2, the full RF power may be delivered to the catheter tip(see block 520). In other words, at least initially, the system may stopdelivering pulsed RF energy to the ablation tip as the system tries todrive the tip temperature from the set point 1 temperature to the setpoint 2 temperature. In block 522, the system monitors the tiptemperature. In decision block 524, the system compares the temperatureat the ablation tip to set point 2. If the tip temperature is not yetapproximately equal to the value of set point 2, the system repeatedlyreturns to block 522 and continues to monitor the tip temperature beingreported to the pulse control box. Once the tip temperature isapproximately equal to the value of set point 2, control transfers fromblock 524 to block 526 in FIG. 5.

Block 526 is similar to block 516 and, at this point, the control systembegins again to pulse the delivery of RF energy in an effort to keep thetip temperature approximately at set point 2 without overheating thetissue. In decision block 528, the system next attempts to determinewhether the ablation is complete (e.g., a physician may stop calling forthe delivery of ablation energy). Once it is determined that theablation is complete (e.g., when, a physician determines that sufficientRF energy has been delivered to the tissue), control transfers to block530; and all delivery of RF energy to the ablation tip is stopped.

As mentioned, in one of the sample embodiments described herein, the PIDcontroller receives values for set point 1 and set point 2, which may beentered by a user. The PID controller also receives the measuredtemperature (or multiple measured temperatures if multiple temperaturesensors are present) from the catheter tip. The controller thendetermines when to permit delivery of full power RF energy or pulsed RFenergy to the ablation tip, including, in the latter case, the length ofthe pulses (i.e., the time periods when RF energy is being delivered tothe catheter tip) and the length of the time periods when no RF energyis being delivered to the catheter tip. The length of the pulses and thelength of the non-pulse time periods may vary continuously. That is, theduration of two adjacent pulses may be different, and the length of twoadjacent non-pulse time periods may be different. The PID controllerdetermines algorithmically when to turn the RF power “on” and “off” asit receives real-time (or near-real-time) tip temperature feedback fromthe ablation catheter.

FIG. 6 depicts six representative controller response curves, showinghow a measured process variable (which may be the measured tiptemperature in the control systems disclosed herein) may approach a setpoint (which may be the desired tip temperature in the control systemsdisclosed herein), depending on how the controller is configured. In theablation controllers discussed herein, the controller response curvelabeled “Long Integral Action Time” in FIG. 6 may be a desirablecontroller response as the tip temperature is driven from its startingtemperature to the desired ablation temperature. In particular, in thiscurve, which is located in the middle of the left three curves in FIG.6, the temperature would never exceed the set point temperature (e.g.,set point 1 or set point 2 in FIG. 5), but would reach the set pointtemperature in a timely and efficient manner.

FIG. 7 depicts a representative controller response curve and depictshow a measured process variable (PV) at a first set point (“initialsteady state value of PV”) may be driven to a second set point (“finalsteady state value of PV”). This ‘dual set point’ configuration isrepresented in the full flowchart of FIG. 5, which is described above.It should be noted, however, that such a dual set point control schemeis not required. In other words, an effective controller could drive thecatheter tip temperature directly to the set point ultimately desired,without driving to a first value (e.g., set point 1) and then driving toa second value (e.g., set point 2). Hence, blocks 518-526 are labeled“optional” in FIG. 5. If these five blocks were not present, the “No”decision line from block 528 would go to block 516. The control systemwould then be configured to drive to a single set point. That said,there are potential advantages to keeping all blocks of the controlscheme depicted in FIG. 5. For instance, the control system of FIG. 5may have some distinct safety advantages. For example, set point 1 couldbe an initial temperature that is somewhere between the startingtemperature of the ablation tip and the ultimate desired temperature forthe ablation tip. If the system is able to reach the set point 1 valueeffectively and while remaining under control, that would provide theuser with confidence that the tip is in contact with the tissue and thatthe controller is working properly before the tip temperature reaches apotentially dangerously-high temperature. Once set point 1 is reached(i.e., where control transitions from block 514 to block 516 in FIG. 5),the user with have confidence that the controller is functioningproperly and could then, at block 518 of FIG. 5, input a higher(ultimately desired) working temperature for creating lesions.

To enable the ablation temperature control system described above towork most effectively, it may be desirable to have an ablation tiphaving a relatively low thermal mass (also known as ablation tip havinghigh thermal sensitivity). If the ablation tip has a relatively lowthermal mass, it more rapidly heats (i.e., it comes to temperaturequickly) and cools (i.e., it does not remain hot for long after power isremoved), enabling tighter control of the tip temperature and less“coasting” of the tip temperature past a desired set point as well asmore rapid reduction in tip temperature when RF power is removed fromthe tip. In fact, such a tip may cool down at the same rate as thetissue, which would inform the user whether the tip became dislodgedduring ablation. Remaining FIGS. 8-25, which are described furtherbelow, depict various embodiments and components of ablation cathetertips that can be used effectively with the pulsed RF control systemsdescribed herein. The catheter tips disclosed herein are not necessarilythe only tips that could be used with the pulsed RF control systemsdescribed herein.

FIG. 8 is a fragmentary, isometric view of various components comprisingan embodiment of a tip 42 at the distal end of an ablation catheter thatcould be used with the pulsed RF control systems disclosed herein. Inthis embodiment, a conductive shell 44 (e.g., a platinum shell, aplatinum iridium shell, or a gold shell) with irrigation ports or holesis present at the most distal end of the catheter components shown inFIG. 8. The conductive shell 44 (which may weigh, for example, 0.027 g)includes a shell distal end portion 48 and a shell proximal end portion50, which may comprise one or more parts or components. In thisparticular embodiment, the shell 44 includes six irrigation holes 46,two of which are visible in this isometric view. Also visible in FIG. 8is an optional shank 52 comprising an annular or washer-shaped brim 54and a cylindrical open crown 56, which together define thetop-hat-shaped shank. In this embodiment, the conductive shell 44 andthe shank 52 effectively encase an ablation tip insert 58, the proximalsurface 60 of which is partially visible in FIG. 8. An electrical leadwire 62 is shown connected (e.g., by soldering or welding) to the shank52. Alternatively, the electrical lead wire 62 may be directly connectedto the conductive shell 44. A number of lead wire pairs 64 for thetemperature sensors comprising part of the tip may be seen extendingrearwardly or proximally in FIG. 8. Finally, FIG. 8 also shows twocomponents of an irrigation tube assembly 66 extending proximally inFIG. 8 (i.e., rightwardly in this figure). Although the conductive shell44 depicted in the figures includes six irrigation holes 46, more orfewer holes may be used, and the size of the holes may be larger, orsmaller, or a mix of larger and smaller holes.

Using the control systems described herein, it may be completelyunnecessary to irrigate the ablation tip. FIG. 9 is similar to FIG. 8,but the conductive shell 44′ depicted in FIG. 9 does not include anyirrigation ports or holes through it (compare element 46 in FIG. 8).Thus, this is a non-irrigated catheter tip 42′ that could be used incombination with the pulsed RF control systems described herein. Most ofthe discussion below focuses on the irrigated catheter tip embodiment 42of FIG. 8, but much of what is said below regarding the embodiment 42depicted in FIG. 8 applies equally well to the non-irrigated cathetertip embodiment 42′ depicted in FIG. 9, with the exception of thediscussion of the irrigation features. It should also be noted that,although the irrigation tube assembly 66 (shown in FIG. 8) is notnecessary in the non-irrigated catheter tip embodiment 42′ depicted inFIG. 9 (and, thus, is not shown in FIG. 9), the irrigation tube assembly66 could be present on the non-irrigated catheter tip embodiment.Further, as also shown in FIG. 9, the proximal surface 60′ of theablation tip insert of the non-irrigated embodiment 42′ may be slightlydifferent from the proximal surface 60 (FIG. 8) of the ablation tipinsert 58 (see also FIG. 10) of the irrigated embodiment 42 (FIG. 8). Inparticular, the proximal surface 60′ may not include the main channel84, which is discussed further below in connection with FIG. 10. Thenon-irrigated embodiment of FIG. 9 could, however, just as easily usethe same ablation tip insert 58 and the irrigation tube assembly 66shown in the irrigated catheter tip embodiment 42 of FIG. 8, which wouldmake it possible, for example, to manufacture both irrigated andnon-irrigated embodiments on a single assembly line, and would likelyresult in the two embodiments exhibiting more similar structuralintegrity during use.

FIG. 10, which is an exploded, isometric view of the catheter tip 42depicted in FIG. 8, is described next, starting with the elements shownin the upper left-hand portion of that figure and working toward thelower right-hand portion of the figure. FIG. 10 again depicts theconductive shell 44, but this time exploded away from the othercomponents of the tip shown in FIGS. 8 and 10, thereby revealingadditional features and components. To the right of the conductive shellin FIG. 10 is an assembly of an ablation tip insert 58 and onetemperature sensor 68 (e.g., a thermocouple). As may be seen in FIG. 10,the tip insert 58 includes a plurality of lateral irrigation channels 70that are sized and arranged to align with complementary irrigation holes46 through the conductive shell 44. To facilitate assembly, the diameterof the lateral irrigation channels 70 in the tip insert 58 may besmaller than the complementary holes 46 through the conductive shell 44.Thus, it would be less critical to precisely align the lateralirrigation channels with the holes through the conductive shell duringmanufacturing, and the exiting irrigant would have less of anopportunity to contact the conductive shell before reaching a bloodpool.

The tip insert, which may be a unitary piece, includes a main body 72and a stem 74. The tip insert 58 can be constructed from, for example,plastic (such as PEEK, which is polyether ether ketone) orthermally-insulative ceramic. In the depicted embodiment, the main bodyportion 72 includes a plurality of optional, longitudinally-extendingsensor channels or ditches 76. In FIG. 10, a thermal sensor 68 is shownmounted in one of these ditches 76. Each of the sensor ditches isseparated from the next adjacent sensor ditch by alongitudinally-extending shell seat 78. The plurality of shell seatsbetween the sensor ditches are configured to ride against, or very nearto, the inner surface of the conductive shell 44. Similarly, the stem 74of the tip insert 58 defines a plurality of longitudinally-extendingwire channels or ditches 80 separated by a plurality oflongitudinally-extending shank seats 82. The ditches 76, 80 areconfigured to carry temperature sensor lead wires on their path to theproximal end of the catheter. The shank seats 82 are sized andconfigured to ride against, or very near to, the inner surface of thecylindrical open crown portion 56 of the shank 52. The tip insert 58includes a main channel 84 having a circular cross-section that, asshown in the figures and as described further below, may include morethan one inner diameter.

Downward to the right of the tip insert 58 in FIG. 10 is an irrigationtube assembly 66. The irrigation tube assembly comprises, in thisembodiment, a central irrigation tube 86 and an optional seating sleeve88. The central irrigation tube 86 has a distal end 90 and a proximalend 92 and may be constructed from a polymer, such as polyimide. Thiscentral irrigation tube may extend proximally toward a catheter handle,or may extend proximally all the way to the catheter handle. Theoptional seating sleeve 88, as shown in the embodiment depicted in FIG.10, may include a cylindrical portion and a frustoconical boss. Theseating sleeve may be positioned at a desired longitudinal locationalong the outer surface of the central irrigation tube 86 and then maybe fixed in place (for example, by an adhesive or sonic welding or viasome other technique). The irrigation tube assembly would then bemounted in the tip insert by, for example, adhesive. If the optionalseating sleeve is not included (e.g., to simplify tip construction andmanufacturing), the central irrigation tube 86 could be adhered directlyto the tip insert 58. To the right of the irrigation tube assembly inFIG. 10 is the optional shank 52. Details of the shank are describedfurther below in connection with, for example, FIG. 14. To the right ofthe shank are five additional temperature sensors 68. In particular, inthis particular embodiment of the tip, six temperature sensors areradially disposed symmetrically about the catheter longitudinal axis 94(see, for example, FIG. 8). Since one of those six thermal sensors isdepicted already in position on the tip insert 58 in FIG. 10, theremaining five temperature sensors are shown in the lower right-handportion of FIG. 10, oriented and arranged so as to slip into theremaining five complementary sensor ditches 76 formed in the tip insert.

FIGS. 11-13 are additional views of the conductive shell 44 depicted in,for example, FIGS. 8 and 10. As shown in these figures, the conductiveshell may comprise a hemispherical or nearly-hemispherical domed distalend 48 and a cylindrical body 50. In the figures, a ‘seam’ 96 is shownbetween the domed distal end 48 and the cylindrical body 50. This may bemerely a circumferential transition line between the cylindrical bodyand the domed distal end of a unitary component; or, alternatively, itmay be the location where the cylindrical body is connected to the domeddistal end by, for example, welding. In one embodiment, the wallthickness 98 of the shell is 0.002 inches, but alternative wallthicknesses also work. The conductive shell could be formed ormanufactured by, for example, forging, machining, drawing, spinning, orcoining. Also, the conductive shell could be constructed from moldedceramic that has, for example, sputtered platinum on its externalsurface. In another alternative embodiment, the conductive shell couldbe constructed from conductive ceramic material.

FIG. 14 is an enlarged, isometric view of the shank 52 also depicted in,for example, FIGS. 8-10. The brim 54 may include a circumferentialoutward edge 100 that, as described below, may be connected by weldingor soldering to a surface (e.g., the inner surface) of the cylindricalbody 50 of the conductive shell. The shank includes a cylindrical opencrown 56 that also defines an inner surface. As described above, theinner surface of the cylindrical open crown is sized and configured toslide over the shank seats 82 defined on the stem of the tip insert 58.The cylindrical open crown of the shank also defines a proximal end oredge 102.

FIG. 15 is an isometric, cross-sectional view of various components ofthe catheter tip 42 also depicted in FIG. 8 and clearly shows twotemperature sensors 68 mounted in their respective temperature sensorditches 76. As may be clearly seen in this figure, the sensor ditchesmay include a wire ramp 104 that allows the thermal sensor lead wires 64to transition from the sensor ditches 76 (formed in the main body of thetip insert) to the wire ditches 80 (formed in the stem of the tipinsert). In this configuration, the circumferential outer edge 100 ofthe brim 54 of the shank 52 is shown riding against the inner surface ofthe cylindrical body of the conductive shell 50. The shank may be weldedor soldered to the conductive shell at this interface to ensure goodelectrical contact between the shank and the shell. In particular, sincethe tip electrode lead wire 62 may be electrically connected to thecylindrical open crown 56 of the shank 52 in this embodiment, the shankmust be conductively connected to the conductive shell 44 in a mannerthat permits transfer of energy from the tip electrode lead wire 62 tothe shank 52 and then to the conductive shell 44.

Looking more closely at the irrigation tube assembly 66 shown in FIG.15, it is possible to see that the distal end 90 of the centralirrigation tube 86 rides against an inner annular ledge 106 formed aspart of the tip insert 58. Further, the frustoconical boss defines adistally-facing ledge or lip that rides against the distal end of thestem 74 of the tip insert 58. Thus, the irrigation tube assembly seatsagainst both the proximal surface 60 of the tip insert 58 as well as theinner annular ledge 106 defined along the longitudinal irrigationchannel 84 extending through most of the tip insert 58. It should benoted that when the temperature sensors are in place in the tip insert,when the irrigation tube assembly is mounted in the tip insert, and whenthe conductive shell and the shank are in position, any voids in theassembled tip (other than the lateral irrigation channels 70) may befilled with potting material, providing a durable assembled set ofcomponents. It should also be noted that the outer surface of thetemperature sensors are mounted so as to at least be in close proximityto, and preferably so as to be in physical contact with, the innersurface of the conductive shell 44. As used herein, “in close proximityto” means, for example, within 0.0002 to 0.0010 inches, particularly ifa conductive adhesive or other bonding technique is used to bond thetemperature sensors to the inner surface of the shell. Depending on thespecific properties of the sensors, the construction and materials usedfor the shell, and the type of conductive adhesive or the other bondingtechnique employed, it is possible that enough temperature sensitivitymay be achieved despite even larger gaps between the sensors and theconductive shell, as long as the sensors are able to readily sense thetemperature of the tissue that will be touching the outer surface of theconductive shell during use of the catheter tip. Also, the distal endportions of the sensor ditches 76 may be shallower than the proximal endportions of the sensor ditches. In this manner, when a temperaturesensor 68 is mounted in its respective sensor ditch, the distal mostportion of the temperature sensor is “lifted” toward and possiblyagainst the inner surface of the cylindrical body of the conductiveshell 44. This helps to establish good thermal conductivity between theconductive shell and the thermal sensor or sensors mounted inside of theshell.

FIG. 16 is similar to FIG. 15, but is a cross-sectional view taken at aslightly different angular orientation from that shown in FIG. 15, tothereby reveal two of the lateral irrigation channels 70 configured todeliver irrigant 108 outside of the tip 42. Since the conductive shellis very thin in these embodiments, and since the tip insert isconstructed from an insulative material, the irrigant, when used, hasvery little ability or opportunity to influence the temperature of theconductive shell 44. As shown to good advantage in FIG. 16, the irrigantexiting the lateral irrigation channels touches the inner edges of theholes 46 through the conductive shell before exiting to the surroundingblood. This may be contrasted to what is shown in FIG. 18, which depictsa prior art catheter tip 42″. In particular, FIG. 18 depicts a solidplatinum (or platinum iridium) tip 110 with a polymer irrigation tube 86mounted in it. In this solid platinum tip (which may weigh, for example,0.333 g), the irrigant 108 flows through and directly contacts a portionof the platinum tip before reaching the lateral irrigation channels 70′and then exiting the tip. Thus, there is a relatively extended period oftime where the cool irrigant rides directly against the platinumcomprising the conductive tip. Thus, in the embodiment depicted in FIG.18, the irrigant has a much greater opportunity to influence thetemperature of the tip than does the irrigant in the embodiment depictedin, for example, FIG. 16.

Also, during ablation with a solid platinum tip 110, essentially theentire tip must heat up before a sensor embedded in the tip senses atemperature rise. Thus, not only does the portion of the tip in contactwith the tissue being treated heat up, but also the entire tip gets hot,even portions of the tip that are remote from the tissue being treated.Blood flow around the entire solid platinum tip robs heat from the tip,which further distorts the temperature sensed by a sensor embedded inthe solid platinum tip; and temperature averaging issues may come intoplay. For at least these reasons, the temperature sensor embedded in asolid platinum tip is less capable of accurately reporting thetemperature in the immediate vicinity of the tissue being treated. Incontrast, in embodiments such as the one depicted in FIGS. 15 and 16,with a relatively thin conductive shell 44 surrounding an insulative tipinsert 58, the temperature of the conductive shell in the immediatevicinity of the tissue-tip interface heats up quickly, and the sensor 68closest to that portion of the conductive shell rapidly senses andreports a temperature rise in the immediate vicinity of the tissue-tipinterface. It is not necessary for the entire tip to heat up before thesensor can report a temperature rise in the tissue, the blood flowingaround the entire tip thus has less of an opportunity to distort thesensed tip temperature, and fewer temperature averaging issues come intoplay.

FIG. 17 is an enlarged, fragmentary, cross-sectional view showing onepossible interconnection between the cylindrical body 50 of theconductive shell 44, the shank 52, and the RF lead wire 62. As shown inthis figure, a proximal edge 112 of the cylindrical body 50 of theconductive shell is bent around the circumferential outward edge 100 ofthe shank brim 54. The shank brim and the shell body are then connectedby welding or soldering, for example. Thus, energy coming from the RFlead wire 62 can be delivered to the shank crown 56, conducted to theshank brim 54, and then delivered to the cylindrical body 50 of theconductive shell.

FIG. 19 is similar to FIGS. 15 and 16, and depicts another fragmentary,isometric, cross-sectional view, but this time taken from an angularorientation that clearly shows a distal-most thermal sensor 114. Inparticular, this figure clearly depicts an arc-shaped channel extension116 extending from one of the sensor ditches 76. As shown in thisembodiment, the distal-most thermal sensor (i.e., a seventh thermalsensor in this embodiment) can thus be placed very near to the mostdistal portion of the tip 42. This distal-most thermal sensor is shownhaving a spherical shape in FIG. 19 and being placed ahead of (i.e.,distally of) one of the radially-disposed thermal sensors 68.

FIG. 20 is an isometric view of components of the tip also depicted in,for example, FIGS. 8, 10, 15, 16, and 19. In this figure, all six of theradially-disposed thermal sensors 68 are in place in their respectivesensor ditches 76. The seventh, distal-most thermal sensor may also bein place, but is not shown in this particular figure. This figure alsoclearly shows the frustoconical boss comprising part of the optionalseating sleeve 88 with its distally-facing surface or tip restingagainst the proximally-facing surface 60 of the tip insert 58.

FIG. 21 is similar to FIG. 20, but shows components of the catheter tipfrom a different view, wherein the distal-most thermal sensor 114 (i.e.,the seventh thermal sensor in this embodiment) is visible, and this viewalso includes the shank 52, which is not present in FIG. 20. In FIG. 21,the shank is in place over the stem of the tip insert, which helpsclarify the benefit of the wire ramps 104 connecting the sensor ditches76 to the wire ditches, both of which are formed in the tip insert.

FIG. 22 is an isometric view of just the thermally-insulative ablationtip insert 58 also depicted in FIG. 21, but without any other tipcomponents. All of the ablation tip inserts described herein arepreferably constructed from thermally-insulative material. They could beconstructed from, for example, ULTEM. In this particular embodiment, thetip insert includes six laterally-extending irrigation channels 70, eachof which has a longitudinal axis arranged substantially perpendicular tothe longitudinal axis of the tube channel that is itself arrangedsubstantially parallel to the catheter longitudinal axis 94. Thelaterally-extending irrigation channels connect a distal end of the tubechannel 84 to an outer surface of the tip insert. It should be notedthat the laterally-extending irrigation channels could be arranged at adifferent angle (i.e., different from 90°) relative to the tube channellongitudinal axis. Also, more or fewer than six laterally-extendingirrigation channels may be present in the tip insert. Again, the outersurface of the tip insert may define a plurality of sensor ditches 76,and these ditches may be separated by a plurality of shell seats 78.These sensor ditches may be, for example, 0.010 inches deep. The shellseats, as described above, may be configured to ride against, or verynear to, the inner surface of the conductive shell. A few of the sensorwire ramps are also clearly visible in FIG. 22. As previously described,the stem 74 of the tip insert may define a plurality of wire ditches 80separated by a plurality of shank seats 82 as shown in FIG. 22.

FIG. 23 depicts the tip insert 58 of FIG. 22 in a slightly differentorientation, revealing the arc-shaped channel 116 (or sensor ditchextension) that extends toward the distal-most end of the catheter tipto position the distal-most thermal sensor 114 (see, for example, FIG.21) at that location. It should be kept in mind that this arc-shapedchannel extension need not be present. It has been determined, however,that a number of advantages may be realized by positioning a thermalsensor as far distally on the catheter tip as possible. For example, inview of the rapid heat dissipation experienced by these catheter tips,it can be extremely helpful to sense temperature at this distal locationsince it may be in the best location for most accurately determining thetemperature of the surrounding tissue during certain procedures.

FIG. 24 depicts an alternative thermally-insulative ablation tip insert58′. This tip insert could be used in a non-irrigated embodiment of thecatheter tip 42′, such as the embodiment depicted in FIG. 9. Inparticular, as discussed above, the control systems for deliveringpulsed RF to ablation catheters described herein may completelyeliminate the need for the use of irrigation. With that in mind, FIG. 24depicts one possible configuration for a tip insert for use in anon-irrigated ablation catheter. This embodiment of the tip insert stillincludes sensor ditches 76 and sensor wire ditches 80 as describedabove.

Further, it should be understood that, in other embodiments of thethermally-insulative ablation tip insert (both irrigated andnon-irrigated embodiments), there may be more or fewer sensor ditches76. In fact, although the sensor ditches may facilitate placement of thesensors 68 on the insert (e.g., during catheter assembly), the outersurface of the main body of the tip insert may be smooth (or at leastditchless). In such an embodiment, the sensors may be aligned on thesmooth outer surface of the tip insert (and, possibly, held in place by,for example, adhesive). Then, when the conductive shell is in placearound the tip insert and the sensors 68 are in place between the outersurface of the tip insert and the inner surface of the conductive shell,the gaps or voids between the inner surface of the conductive shell andthe outer surface of the tip insert may be filled with material (e.g.,potting material or adhesive). It is worth noting that the sensors maybe put in place before or after the conductive shell is placed over thetip insert. For instance, the sensors may be mounted on (e.g., adheredto) the smooth outer surface of the tip insert forming atip-insert-sensor subassembly. Then, the conductive shell may be placedover that tip-insert-sensor subassembly before the remaining voidsbetween the tip-insert-sensor subassembly and the conductive shell arefilled. Alternatively, the conductive shell may be held in place overthe tip insert while one or more sensors are slid into the gap betweenthe outer surface of the tip insert and the inner surface of theconductive shell. Subsequently, the voids could again be filled. Thesealternative manufacturing techniques apply to all of the disclosedembodiments that comprise sensors mounted between a tip insert and aconductive shell member.

FIG. 25 is most similar to FIG. 8, but depicts one form of analternative embodiment of a catheter tip 42″′ comprising one or moreisolated temperature-sensing islands 118 which, in this embodiment,reside partially on the domed distal end 48′ of the conductive shell 44″and partially on the cylindrical body 50′ of the conductive shell 44″.Each of these temperature-sensing islands 118 is outlined orcircumscribed by a strip of insulative material 120 placed to reduce oreliminate any potential influence from irrigant flowing through thenearby holes 46′ in the conductive shell. In particular, if the cooledirrigant flowing through a hole through the conductive shellmeaningfully reduces the temperature of the conductive shell around thehole, that lower temperature would not be transmitted to a temperaturesensor mounted within the conductive shell below the temperature-sensingisland 118.

Although a single-layer conductive shell 44 (see, e.g., FIGS. 10-13 and15) constructed from a thin layer of gold, for example, may perform inan magnetic resonance (MR) environment without causing undesirable orunmanageable MR artifacts, a conductive shell comprising an outer layerof a paramagnetic material such as platinum or platinum iridium, forexample, may benefit from a multilayer construction as discussed below.

FIG. 26 is most similar to FIG. 12, but depicts a multilayer conductiveshell 44″′. A multilayer conductive shell may have just a multilayercylindrical body portion, just a multilayer domed distal end portion, orboth a multilayer domed distal end portion and a multilayer cylindricalbody. In the embodiment depicted in FIG. 26, both the domed distal endportion 48″′ and the cylindrical body 50″′ have a multilayerconstruction. As shown in this figure, the domed distal end portion 48″′comprises an inner layer 122 and an outer layer 124, and the cylindricalbody 50″′ similarly comprises an inner layer 126 and an outer layer 128.Again, however, it is not a requirement that the domed distal endportion and the cylindrical body must both be constructed with the samenumber of layers or with the same thickness of layers. Also, the wallsof the conductive shell 44′″ may, for example, be of a total thicknessthat is the same as, or nearly the same as, the thickness 98 (see FIG.12) of the single-layer conductive shell 44 described above. Theconductive shell could be formed or manufactured per, for example, thetechniques already described herein.

FIGS. 27A, 27B, and 27C schematically depict various materials orsubstances in a magnetic field (e.g., in an MR environment). Inparticular, FIG. 27A schematically depicts magnetic flux lines reactingto a diamagnetic substance (the lines of force tend to avoid thesubstance when placed in a magnetic field), FIG. 27B schematicallydepicts magnetic flux lines reacting to a paramagnetic substance (thelines of force prefer to pass through the substance rather than air),and FIG. 27C schematically depicts magnetic flux lines reacting to aferromagnetic substance (the lines of force tend to crowd into thesubstance). Platinum iridium (a paramagnetic material) is commonly usedfor constructing catheter tips. Thus, as may be discerned from lookingat FIG. 27B, a thin conductive shell (e.g., conductive shell 44 depictedin FIG. 12) constructed entirely from platinum or platinum iridium (orsome other paramagnetic material) may induce MR artifacts.

As mentioned above, a more MR compatible catheter tip may comprise, forexample, a single layer conductive shell 44 constructed entirely from adiamagnetic material (e.g., a thin gold conductive shell) or amultilayer conductive shell 44″′. In one example of an MR compatiblemultilayer conductive shell, the conductive shell 44′″ comprises a shelldistal end portion (shown as domed distal end 48″′ in FIG. 26) and ashell proximal end portion (shown as cylindrical body 50″′ in FIG. 26).In this embodiment, the conductive shell 44″′ may comprise a platinumiridium outer layer (or skin) 124, 128 and an inner layer (or liner orcore) 122, 126 constructed from a diamagnetic material (e.g., gold orcopper). In such an embodiment, the paramagnetic outer layer 124, 128and the diamagnetic inner layer 122, 126 ‘cooperate’ in a manner thatminimizes or mitigates against the generation of undesirable MRartifacts. In some multilayer embodiments (e.g., with a paramagneticouter layer and a diamagnetic inner layer), it can be beneficial to massbalance or volume balance the material comprising the layers of themultilayer conductive shell 44″′. Alternatively, the multilayerconductive shell 44′″ of the MR compatible catheter tip may have anouter layer constructed from a diamagnetic material (such as bismuth orgold) and an inner layer constructed from a paramagnetic material (suchas platinum or platinum iridium).

In yet another embodiment (not shown), a multilayer conductive shell maycomprise more than two layers. For example, the conductive shell maycomprise three layers, including a very thin outer layer of aparamagnetic material, a somewhat thicker or much thicker intermediatelayer of a diamagnetic material, and an oversized internal layer of anon-precious metal (or plastic or other material) sized to ensure thatthe finished geometry of the overall ablation tip is of a desired sizefor effective tissue ablation.

Materials that could be used for the inner layer or liner include, butare not limited to, the following: silicon (metalloid); germanium(metalloid); bismuth (post transition metal); silver; and gold. Silverand gold are examples of elemental diamagnetic materials that haveone-tenth the magnetic permeability of paramagnetic materials likeplatinum. Thus, one example multilayer shell configuration couldcomprise a platinum outer layer (or skin) and an inner layer (or lineror core) of gold or silver with a thickness ratio (e.g.,platinum-to-gold thickness ratio) of at least 1/10 (i.e., the platinumlayer being one-tenth as thick as the gold layer). In another example, amultilayer conductive shell configuration 44″′ could comprise a platinumouter layer and a bismuth inner layer with a thickness ratio (e.g.,platinum-to-bismuth thickness ratio) of at least ½ (i.e., the platinumouter layer being one-half as think as the bismuth inner layer) sincebismuth has a permeability that is about one-half the permeability ofplatinum. The layers may also be constructed from alloys, which may beused, for example, when a pure element material might otherwise bedisqualified from use in the construction of a catheter tip.

FIG. 28 is most similar to FIG. 20, but depicts an embodiment havingboth distal temperature or thermal sensors 68 and proximal temperatureor thermal sensors 68′ mounted on a tip insert. As depicted in FIG. 28,a plurality of temperature sensors 68′ may be deployed around or nearthe proximal end of the tip 42. These temperature sensors 68′ could bemounted, for example, on the ablation tip insert as already describedabove. Although FIG. 28 depicts an ablation tip insert 58 for anirrigated tip 42, the proximal temperature sensors 68′ may also be usedin non-irrigated embodiments such as the tip 42′ depicted in FIG. 9. Theproximal thermal sensors 68′ may be deployed, for example, in anangularly-spaced configuration similar to the configuration of the sixradially-disposed distal temperature sensors 68 shown in, for example,FIGS. 15, 19, 20, and 21 (but located near the proximal end of the mainbody 72 of the ablation tip insert 58 rather than its distal end). Thetemperature sensor configuration depicted in FIG. 28 would provide ahigher-resolution ‘picture’ of the thermal profile of the tip and,therefore, a better understanding of tissue temperature near thecatheter tip during ablation. This is particularly beneficial when sucha tip construction is used with the pulsed RF control systems disclosedherein.

FIG. 29A is a top view of a multi-layer flexible circuit 290, consistentwith various aspects of the present disclosure. In various embodiments,the multi-layer flexible circuit 290 may be installed on a tip insert ofa catheter tip assembly instead of utilizing individually wiredtemperature sensors and electrophysiology electrodes. By consolidatingthe various wire leads into one or more flexible circuits, or even oneor more flexible circuits plus a few wire leads, the cost, complexity,and manufacturing assembly time associated with such ablation tipassemblies may be greatly reduced. In some specific implementations,lead wire count extending through a catheter shaft of a catheterablation system may be reduced by nearly 50%.

Multi-layer flexible circuit 290 may include one or more connectors 292located at the distal end of a strand of the flexible circuit tofacilitate manufacturability within a catheter tip sub-assembly. Forexample, where the catheter tip is completed in sub-assembly form priorto installation in a catheter shaft sub-assembly, the connectors 292 mayextend from the catheter tip sub-assembly to facilitate coupling toanother flexible circuit, or lead wires extending from the cathetershaft sub-assembly. To further facilitate assembly, the connectors 292may be electrically coupled to the other flexible circuit of thecatheter shaft via an electrical connector. Alternatively, solder padsof the two flexible circuits may be soldered to one another. The use offlexible circuits may also further facilitate automation of the catheterassembly process.

As shown in FIG. 29A, the variation in lengths between connectors 292 ₁and 292 ₂ facilitate assembly where the connectors are coupled to eitherflex circuit cables or to wire leads. Specifically, the longer connector292 ₂ may be electrically coupled to a first flexible circuit cable,after which another flexible circuit cable may be laid over the longerconnector 292 ₂ while electrically coupled to the shorter connector 292₁. Such an assembly process facilitates the use of a single, compactlumen extending through the catheter shaft to carry all of the necessaryelectrical wiring.

In FIG. 29A, electrical signals from distal and proximal thermocouples68 and 68′ on flexible circuit 290 are isolated from one another byextending traces 296 on flexible circuit board 291 from the distalthermocouples 68′ to solder pads 293 _(1-N) on connector 292 ₁, andtraces 296 from the proximal thermocouples 68 to solder pads 291 _(1-N)on connector 292 ₂. This exemplary circuit board routing helps tomitigate electrical and electromagnetic cross-talk (interference)between the un-shielded electrical traces.

In various embodiments, flexible circuit 290 may further include one ormore electrical contacts 294 ₁₋₃(for electrically coupling to spotelectrodes 328; see, e.g., FIG. 32), as shown in FIG. 29A. Theseelectrodes, when capacitively coupled to a conductive shell, whichencompasses at least a portion of a tip insert, may collectelectrophysiology data related to tissue (e.g., myocardial tissue) incontact with (or in close proximity to) the conductive shell. Thiselectrophysiology data is then communicated via traces 296 to one ormore solder pads 291 and 293 on the connectors 292.

To facilitate coupling of flexible circuit 290 to a tip insert or otherstructure, vias 295 may extend through the flexible circuit board 291.In such embodiments, a protrusion may extend out from an externalsurface of a tip insert, and extend through the mating vias 295 in theflexible circuit board 291. Once properly located, the protrusions maybe heat staked to create an interference fit between the via and theprotrusion to permanently couple them. In the alternative, the flexiblecircuit board 291 may include bonding locations that facilitate suchcoupling. It is to be understood that various coupling means may beutilized, including: ultrasonic welding, fasteners, adhesives, frictionand compression fits, etc. to achieve coupling of the flexible circuitboard 291 to the tip insert. In yet further embodiments, to facilitateelectrical and thermal coupling between thermocouples 68 and 68′, spotelectrodes, and an inner surface of a conductive shell, thethermocouples and electrophysiology electrodes may be directly coupledto the conductive shell. Thereby obviating any precise fitting requiredbetween the thermocouples, electrophysiology electrodes, and theconductive shell. In various embodiments consistent with the presentdisclosure, a quick thermal response of the thermocouples is desirableto provide an ablation control system with control inputs with as littlelag as possible. Slow thermal response of the thermocouples may causeover ablation of tissue, for example.

When flexible circuit 290 is wrapped around a tip insert, distalthermocouples 68 from a first distal circumferentially-extending ringnear a tip of the catheter. Similarly, proximal thermocouples 68′ from asecond proximal circumferentially-extending ring, distal from the tip ofthe catheter relative to the first distal ring. Thermocouple 114 iswrapped around a distal radius of the catheter tip, and is thereby thedistal most thermocouple.

It is to be understood that various circuit board layouts may beutilized to facilitate application specific design constraints invarious flexible circuit 290 designs consistent with the presentdisclosure. For example, to limit circuit board area, additional PCBlayers may be added where the Z-dimension of a given application allows.Similarly, more or less connectors 292 may be implemented. In yetfurther embodiments, wireless communication circuitry and/or a powersupply may be embedded on the flexible circuitry 290 to alleviate theneed for electrical connections running the length of the catheter shaftaltogether.

As more clearly shown in reference to FIGS. 29B and 29C, flexiblecircuit board 291 may include three layers: a copper layer at a topsurface, an intermediate polyimide layer, and a constantan layeropposite the cooper layer. Each of the thermocouples 68 and 68′ may beformed by drilling a via through the copper, polyimide, and constantanlayers, and through plating the via with copper. Various thermocoupledesigns and manufacturing methods are well known in the art. Either sideof the thermocouple is then electrically coupled to a trace on itsrespective layer. The voltage across the two traces may be compared, andthe resulting voltage change is indicative of a temperature of aconductive shell thermally coupled to the thermocouple. In variousapplications, including ablation therapies, as the conductive shell isin direct contact with tissue being ablated, efficacy of an ablationtherapy may be surmised.

In the present embodiment, flexible circuit 290 is designed tofacilitate individual addressability of each of the thermocouples 68 and68′, and electrical contacts 294. In more simplified embodiments, thethermocouples 68 in a distal circumferential ring may be electricallycoupled in parallel to effectively facilitate temperature averaging ofthe thermocouples, and to minimize printed circuit board 291 size. Suchan embodiment may be particularly useful in applications wheredetermining a tissue contact point along a circumference of the ablationcatheter is not necessary. The present embodiment may also limit theeffect of minute hot zones on an ablation control system.

As shown in FIG. 29A, each thermocouple (68 and 68′) is positioned on asmall protrusion extending from a body of flexible circuit board 291.Each of the protrusions facilitate positive positioning of the flexiblecircuit board when assembled to a tip insert which has mating channelfeatures (76 and 76′, as shown in FIG. 30), thereby preventing movementof the flexible circuit board relative to the tip insert. Such movementmay otherwise affect thermal coupling of the thermocouples to an innersurface of a conductive shell. Similarly, thermocouple 114 also extendsout onto a larger protrusion of the flexible circuit board, facilitatingplacement of the thermocouple 114 at the distal most tip of thecatheter.

FIG. 29B is a top view of a top copper layer 300 of the multi-layerflexible circuit 290 of FIG. 29A, consistent with various aspects of thepresent disclosure. The top copper layer is placed above the two otherlayers of the flexible circuit board—polyimide, and constantan layers.As shown in FIG. 29A, non-electrical vias (through-holes) 295 extendthrough all three layers of the flexible circuit board and provide ameans for coupling the multi-layer flexible circuit 290 to a tip insert.The top copper layer contains signal traces 296 _(A) which areelectrically coupled to a hot junction 302 ₁₋₂ for each of thethermocouples. As is well known in the arts, thermocouples typicallycomprise two dissimilar metals joined together at respective ends of thedissimilar metals. The end of the thermocouple placed into thermalcontact with a hot object is called the hot junction 302 ₁₋₂, while theopposite end, which is disposed to a base-line temperature within thetip insert, is a cold junction (for example, 312 ₁₋₃, as shown in FIG.29C). The hot junction in the top copper layer and the cold junction inthe constantan layer is electrically coupled to one another through thepolyimide layer. When a catheter tip consistent with the presentembodiment is placed against a warm object, such as myocardial tissuebeing ablated by pulsed radio frequencies, a voltage difference acrossthe hot and cold junctions develops. The voltage difference iscorrelated with a temperature of the hot junction. The materials of thehot and cold junctions may include one or more of the followingmaterials: iron, nickel, copper, chromium, aluminum, platinum, rhodium,alloys of any of the above, and other metals with high conductivity.

As each spot electrode (which is electrically coupled to one ofelectrical contacts 294 ₁₋₃) forms only one half of a circuit, eachelectrode need only one trace 296 extending to a connector 292 of theflexible circuit. Accordingly, no electrical traces extend from theelectrode pads 301 of the electrode, as traces (as shown in FIG. 29C) onthe constantan layer electrically couple the spot electrodes to aconnector 292 of a connector pad 293. When assembled in a catheter, theelectrode pads 301 are electrically coupled to a conductive shell of acatheter tip to allow for electrical signals from tissue in contact withthe conductive shell to travel through to the electrode pads 301. Theelectrical signals from each spot electrode are compared and analyzed todetect electrophysiological characteristics indicative of medicalconditions, such as, atrial fibrillation. Similarly, during and aftertreatment, the electrodes may be used to conduct diagnostics anddetermine an efficacy of a treatment.

FIG. 29C is a top view of a bottom constantan layer 310 of a multi-layerflexible circuit 290 of FIG. 29A, consistent with various aspects of thepresent disclosure. Electrical traces 296 _(B) extend between coldjunctions 312 ₁₋₃ and connector pads 293 _(1-N) of a connector 292.Similarly, electrical traces 296 _(B) extend between electrical nodes311 (which are electrically coupled to spot electrodes) and connectorpads 293 _(1-N) of the connector 292. In the present embodiment, all ofthe cold junctions 312 _(1-N) are electrically interconnected, andeffectively function as a common ground for each of the thermocouples.By electrically interconnecting each of the electrical traces extendingfrom the cold junctions, the number of common connector pads 293 _(1-N)may be greatly reduced. As shown in the present embodiment, the commonground for all of the thermocouples requires only a single connector padand reduces the circuit board size and complexity.

FIG. 30 depicts an isometric view of a tip insert 58, consistent withvarious aspects of the present disclosure. The tip insert 58 isconfigured to receive a flexible circuit and to couple the flexiblecircuit about a circumference of the tip insert. In this particularembodiment, the tip insert 58 includes six laterally-extendingirrigation channels 70, each of the irrigation channels 70 have alongitudinal axis arranged substantially perpendicular to thelongitudinal axis of the tube channel 84 that is itself arrangedsubstantially parallel to the catheter longitudinal axis 94 (as shown inFIG. 22, for example). The laterally-extending irrigation channels 70connect a distal end of the tube channel 84 to an outer surface of thetip insert 58. It should be noted that the laterally-extendingirrigation channels could be arranged at a different angle (i.e.,different from 90°) relative to the tube channel longitudinal axis.Also, more or fewer than six laterally-extending irrigation channels maybe present in the tip insert.

As shown in FIG. 30, the outer surface of the tip insert includes aflexible circuit ditch 320 that is configured to receive a flexiblecircuit. The flexible circuit ditch 320 may be, for example, 0.010inches deep to facilitate precise z-height placement of the flexiblecircuit for desirable thermal coupling characteristics betweenthermocouples on the flexible circuit and a conductive shell that isplaced over the tip insert 58.

In various embodiments, to further assist longitudinal and radialplacement of the flexible circuit within the flexible circuit ditch 320,the flexible circuit ditch 320 may include longitudinally extending andradially offset channels 76 _(1-N) and 76′_(1-N) on both proximal anddistal ends (or just one end) of the flexible circuit ditch 320. Thechannels 76 _(1-N) and 76′_(1-N) facilitate precise positioning of theflexible circuit in both longitudinal and radially directions along theflexible circuit ditch 320. This may be particularly desirable wherethermocouples on the flexible circuit are aligned withtemperature-sensing islands on the conductive shell. Connectors 292extending from a main body portion of flexible circuit 290 (as shown inFIG. 29A, for example) may be routed through main body connector ditch325 in a proximal direction (away from main body portion 72), and ontostem 74 of the ablation insert 58. To continue to facilitate routing ofthe connectors 292 on the stem 74, a stem connector ditch 330 extendsalong a length of the stem 74. A ramp is also visible in FIG. 30 betweenmain body connector ditch 325 and stem connector ditch 330, and furtherfacilitates routing of the connector between the main body 72 and stem74.

The isometric orientation of FIG. 30 reveals an arc-shaped channel 116(or sensor ditch extension) that extends toward the distal-most end ofthe catheter tip to position the distal-most thermal sensor 114 at thatlocation (see, for example, FIG. 31). It should be kept in mind that notall embodiments of the present disclosure will include this arc-shapedchannel extension. However, a number of advantages may be realized bypositioning a thermal sensor as far distally on the catheter tip aspossible. For example, in view of the rapid heat dissipation experiencedby catheter tips, it can be extremely helpful to sense temperature atthis distal location since it may be in the best location for mostaccurately determining the temperature of the surrounding tissue duringcertain procedures.

FIG. 31 depicts an isometric front view of a partial catheter tipassembly 42 including a tip insert 58 (as shown in FIG. 30) with amulti-layer flexible circuit 290 (as shown in FIGS. 29A-C) wrappedcircumferentially around the ablation tip insert, consistent withvarious aspects of the present disclosure. Each of the distalthermocouples 68 are located within a channel 76 _(1-N), and each of theproximal thermocouples 68′ are located with a channel 76′_(1-N). Each ofthe distal thermocouples 68 being radially positioned between lateralirrigation channels 70 which are circumferentially distributed about thetip insert 58. Distal tip channel 116 receives a distal tip thermocouple114. To further facilitate coupling of the flexible circuit 290 to thetip insert 58, mating vias 295 may extend through flexible circuit board291. In such embodiments, the tip insert may further include protrusionsthat extend out from flexible circuit ditch 320, align with, and extendthrough mating vias 295 in the flexible circuit board 291. Once properlylocated, the protrusions may be heat staked to create an interferencefit between the via and the protrusion to permanently couple them, or beotherwise coupled.

As further shown in FIG. 31, partial catheter tip assembly 42 includesone or more connectors 292 ₁₋₂ extending in a proximal direction fromthe main body portion of flexible circuit 290 and past shank 52. Theconnectors 292 may be long enough to be routed through an entire lengthof a catheter shaft, or may be a length that facilitates coupling theconnectors 292 to another connector or a plurality of lead wiresextending a length of the catheter shaft.

FIG. 32 depicts an isometric front view, including a partial cut-out, ofthe catheter tip assembly 42 of FIG. 31 with a conductive shell 44encompassing at least a portion of a tip insert and a multi-layerflexible circuit 290, consistent with various aspects of the presentdisclosure. When the conductive shell 44 is installed over the partialcatheter tip assembly 42, irrigation holes 46 are aligned with lateralirrigation channels 70 (as shown in FIG. 31), and thermocouples 68 and68′ on flexible circuit 290 are place into thermal contact with an innerdiameter of the conductive shell 44.

In FIG. 32, electrical contacts 294 on multi-layer flexible circuit 290are positioned below, and in electrically conductive contact with, spotelectrodes 328 on a surface of conductive shell 44. These spotelectrodes 328, depending on the application, may be located across anouter surface of the conductive shell 44, including domed distal end 48.When the spot electrodes 328 are placed into contact with tissue (e.g.,myocardial tissue), the spot electrode receive electrical signalinformation indicative of the health of the tissue in contact therewith,the strength and directionality of electrical signals being transmittedthrough the tissue, among other information that is useful to theclinician to diagnose, treat, and determine patient outcome.

Where catheter tip assembly 42 is an RF ablation catheter, to reduceRF-related interference to the signals received by spot electrodes 328,it may be advantageous to electrically isolate the spot electrodes, fromthe rest of conductive shell 44 and an RF emitter within the cathetertip assembly. Accordingly, the FIG. 32 embodiment includes electricallyinsulative material 320 that at least partially circumscribes spotelectrodes 328 to prevent/limit RF-related signal interference beingreceived by the spot electrodes.

FIG. 33 depicts a top view of an embodiment of a multi-layer flexiblecircuit 330, consistent with various aspects of the present disclosure.The multi-layer flexible circuit 330 includes a flexible circuit board291 with distal temperature sensors 68 ₁₋₆ and proximal temperaturesensors 68′₁₋₆ coupled to an outer layer of the circuit board 291 orbetween layers of the circuit board (where the circuit board layers arethermally conductive). Each of the temperature sensors are electricallycoupled to one or more electrical traces 296 _(1-N) to facilitatecontroller circuitry (electrically coupled to the traces) sampling anelectrical signal from each of the temperature sensors 68 ₁₋₆ and68′₁₋₆. The electrical signals from each of the temperature sensors areindicative of a temperature sensed by the temperature sensor.

The multi-layer flexible circuit 330 of FIG. 33 may be wrapped around atip insert 58 (see, e.g., FIG. 30). The temperature sensors 68 ₁₋₆ and68′₁₋₆ distributed about the surface of the flexible circuit 330facilitate detection of temperatures across a surface of a conductiveshell 44 (see, e.g., FIG. 32) which covers the flexible circuit and isin thermal communication therewith.

The flexible circuit 330 may have one or more legs 331 _(A-B) whichfacilitates the communication of electrical signals from each of thetemperature sensors to a more proximal portion of a catheter shaft towhich the flexible circuit 330 may be coupled. While the one or morelegs 331 _(A-B) of the flexible circuit may extend an entire length ofthe catheter shaft and be directly coupled to controller circuitry, inother embodiments the flexible circuit may only partially extend alength of the catheter shaft and be electrically coupled to one or morelead wires which extend along a remaining length of the catheter shaft.In some embodiments, when the flexible circuit 330 is wrapped around atip insert, the legs 331 _(A-B) may overlap and run along a length ofthe catheter shaft. In other embodiments, it may be desirable to havethe legs 331 _(A-B) of the flexible circuit 330 extend along a length ofthe catheter shaft opposite one another (relative to a longitudinal axisof the catheter shaft).

FIG. 34 depicts a top view of another embodiment of a multi-layerflexible circuit 340, consistent with various aspects of the presentdisclosure. The multi-layer flexible circuit 340 includes a plurality offingers 342 ₁₋₆ that are coupled to one or more legs 341 _(A-B) via abody portion 343. The plurality of fingers 342 ₁₋₆ house distaltemperature sensors 68 ₁₋₆ and proximal temperature sensors 68′₁₋₆. Asdiscussed above in reference to FIG. 33, each of the temperature sensorsare electrically coupled to one or more electrical traces (not shown inFIG. 34) to facilitate sampling an electrical signal from each of thetemperature sensors 68 ₁₋₆ and 68′₁₋₆. The flexible circuit 340, duringassembly to an intravascular catheter, may be wrapped around a tipinsert and sandwiched between the tip insert and a conductive shell. Tofacilitate proper positioning of the temperature sensors on the cathetertip, the tip insert may include channels which the fingers 342 ₁₋₆ maybe positioned within and/or coupled to.

FIG. 35 depicts a top view of yet another embodiment of a multi-layerflexible circuit 350, consistent with various aspects of the presentdisclosure. The multi-layer flexible circuit 350 includes a plurality ofproximal fingers 352 ₁₋₆ and distal fingers 354 ₁₋₆ that are coupled toone or more legs 351 _(A-B) via a body portion 353. The proximal anddistal portions of each finger are coupled to one another via astructural support 355 that prevents undesirable flexure of the fingerswhich can vary the spacing between the temperature sensors mounted onthe fingers. Each of the plurality of proximal fingers 352 ₁₋₆ anddistal fingers 354 ₁₋₆ house proximal temperature sensors 68′₁₋₆ anddistal temperature sensors 68 ₁₋₆, respectively. In the presentembodiment, the structural support 355 houses electrical contacts 294_(1-N). These electrical contacts, when capacitively coupled to aconductive shell which encompasses at least a portion of a tip insert,may collect electrophysiology data related to tissue (e.g., myocardialtissue) in contact with (or in close proximity to) the conductive shell.This electrophysiology data may then be communicated via traces on theflex circuit 350 to controller circuitry.

In various embodiments of the catheter tip assemblies disclosed herein,the catheter tip assemblies may also include a plurality of spotelectrodes on a conductive shell thereof which facilitateelectrophysiology mapping of tissue, such as myocardial tissue, in(near) contact with the shell. In more specific embodiments, theplurality of spot electrodes may be placed across the shell in such amanner as to facilitate Orientation Independent Algorithms which enhanceelectrophysiology mapping of the target tissue and is further disclosedin U.S. application Ser. No. 15/152,496, filed 11 May 2016, U.S.application Ser. No. 14/782,134, filed 7 May 2014, U.S. application Ser.No. 15/118,524, filed 25 Feb. 2015, U.S. application Ser. No.15/118,522, filed 25 Feb. 2015, and U.S. application No. 62/485,875,filed 14 Apr. 2017, all of which are now pending, and are incorporatedby reference as though fully disclosed herein.

Optionally, catheter tip assembly 42 of FIG. 32 may also include one ormore isolated temperature-sensing islands on the conductive shell 44.The one or more isolated temperature-sensing islands are positionedabove thermocouples communicatively coupled to the multi-layer flexiblecircuit 290 and thermally coupled thereto. Each of thesetemperature-sensing islands may be outlined or (partially) circumscribedby a strip of insulative material that reduces or eliminates anypotential influence from irrigant flowing through nearby irrigationholes 46 in the conductive shell. In particular, if cooled irrigant isflowing through a hole in the conductive shell, heat transfer to theirrigant fluid would meaningfully reduce the temperature of theconductive shell around the hole; however, such heat transfer would notinfluence a temperature sensor mounted within the conductive shell belowthe temperature-sensing island. Although the conductive shell 44depicted in the figures includes six irrigation holes 46, more or fewerholes may be used, and the size of the holes may be large, or small, ora mix of large and small holes.

Catheter tips having a variety of thermometry configurations could bedeployed successfully with the pulsed RF control systems describedherein. Thus, although the representative catheter tips described hereininclude six or twelve radially-disposed thermal sensors and one distalthermal sensor placed close to the distal end of the catheter tip, theinvention is not limited to such seven-sensor and thirteen-sensorconfigurations.

Also, catheters comprising various segmented tip designs may work togood advantage with the control systems described above. Some such tipconfigurations are disclosed in U.S. patent application No. 61/896,304,filed 28 Oct. 2013, and in related international patent application no.PCT/US2014/062562, filed 28 Oct. 2014 and published 7 May 2015 inEnglish as international publication no. WO 2015/065966 A2, both ofwhich are hereby incorporated by reference as though fully set forthherein.

It should also be noted that the control systems described herein mayuse a “rolling thermocouple,” which would, for example, measure thetemperature output from each of a plurality of thermocouples every 20msec (for example) and report the highest of these temperatures to thepulse control box and, potentially, directly to the generator (at leastfor safety shutdown reasons). In this manner, and in view of the lowthermal mass of the ablation tips described herein, the controller isalways working with the most accurate representation of the actualtissue temperature. In particular, since the device has low thermalmass, any temperature sensors facing away from the tissue during use ofthe catheter in an ablation procedure would cool rapidly and theirreadings could be ignored or discounted, whereas the temperature sensoror sensors closest to the portion of the catheter tip that is in contactwith tissue would heat rapidly and would, therefore, provide atemperature reading that is closest to the actual temperature of thetissue being ablated. Thus, by using only the temperature reading fromthe hottest temperature sensor (or the two or three hottest temperaturesensors) at any given time, the system is able to rapidly adjust for thewidely varying readings being received from the thermal sensors as thecatheter tip is rotated or pushed into tissue during actual use.

Although several embodiments have been described above with a certaindegree of particularity, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thepresent disclosure. It is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative only and not limiting. Changes in detail orstructure may be made without departing from the present teachings. Theforegoing description and following claims are intended to cover allsuch modifications and variations.

Various embodiments are described herein of various apparatuses,systems, and methods. Numerous specific details are set forth to providea thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “an embodiment,” or the like, means thata particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” “in an embodiment,” or the like, inplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,or characteristics may be combined in any suitable manner in one or moreembodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A high-thermal-sensitivity ablation catheter tip,the tip comprising: an electrically-conductive housing comprising aconductive shell; a thermally-insulative tip insert, wherein theconductive shell surrounds at least a portion of the tip insert; and aflexible electronic circuit distributed around the tip insert, andincluding a plurality of thermal sensors in thermal communication withthe conductive shell and configured to provide directional temperaturefeedback, wherein the plurality of thermal sensors are distributedacross at least one of a length and width of the flexible electroniccircuit, and a wired or wireless communication pathway at leastpartially disposed on the flexible electronic circuit, communicativelyconnected to the plurality of thermal sensors, and configured to reportthe directional temperature feedback to an ablation control system. 2.The high-thermal-sensitivity ablation catheter tip of claim 1, whereinthe flexible electronic circuitry further includes a plurality ofelectrophysiology electrodes in thermal communication with theconductive shell, communicatively connected to the wired or wirelesscommunication pathway, and configured to report data indicative ofelectrophysiology characteristics of tissue in contact with theconductive shell.
 3. The high-thermal-sensitivity ablation catheter tipof claim 1, wherein the plurality of thermal sensors are configured intwo circumferential rings around the tip insert, where the firstcircumferential ring is longitudinally offset relative to the secondcircumferential ring.
 4. The high-thermal-sensitivity ablation cathetertip of claim 1, wherein the conductive shell further comprises an innersurface, and wherein the plurality of thermal sensors are in thermalcommunication with the inner surface of the conductive shell.
 5. Thehigh-thermal-sensitivity ablation catheter tip of claim 1, wherein theplurality of thermal sensors further comprises a distal-most thermalsensor positioned at or near a distal-most end of the conductive shell.6. The high-thermal-sensitivity ablation catheter tip of claim 1,wherein the flexible electronic circuit includes a top copper layer, anintermediate polyimide layer, and a bottom constantan layer.
 7. Thehigh-thermal-sensitivity ablation catheter tip of claim 1, wherein thetip insert includes a ditch that extends into an outer surface of thetip insert, the ditch being configured and arranged to receive theflexible circuit.
 8. The high-thermal-sensitivity ablation catheter tipof claim 1, wherein the conductive shell includes a domed distal end, acylindrical body, and one or more isolated temperature-sensing islands,each of the temperature-sensing islands is confined by a strip ofinsulative material configured to reduce thermal transfer between thetemperature-sensing islands and the conductive shell.
 9. An ablation tipfor an ablation catheter, the ablation tip comprising: a thermally andelectrically conductive housing comprising a conductive shell thatincludes an inner surface; a thermally-insulative tip insert, whereinthe conductive shell surrounds at least a portion of the tip insert; anda flexible electronic circuit circumferentially mounted around the tipinsert and between the conductive shell and the thermally-insulative tipinsert, the flexible electronic circuit including at least three thermalsensors in thermally-transmissive contact with the inner surface of theconductive shell, wherein the at least three thermal sensors areconfigured to receive and report temperature feedback received via theconductive shell, and a wired or wireless communication pathwaycommunicatively connected to the at least three thermal sensors, andconfigured to facilitate reporting of the temperature feedback to anablation control system.
 10. The ablation tip for the ablation catheterof claim 9, wherein the at least three thermal sensors mounted on thetip insert are in physical contact with the inner surface of theconductive shell.
 11. The ablation tip for the ablation catheter ofclaim 9, wherein the flexible electronic circuit further includes aplurality of electrophysiology electrodes in electrically-transmissivecommunication with the conductive shell, communicatively connected tothe wired or wireless communication pathway, and configured to reportdata indicative of electrophysiology characteristics of tissue incontact with the conductive shell.
 12. The ablation tip for the ablationcatheter of claim 9, wherein the thermal sensors are positioned alongthe tip insert in two circumferential rings longitudinally offsetrelative to one another.
 13. The ablation tip for the ablation catheterof claim 9, wherein the flexible electronic circuit includes a topcopper layer, an intermediate polyimide layer, and a bottom constantanlayer.
 14. The ablation tip for the ablation catheter of claim 9,wherein the tip insert includes a ditch that extends along an outersurface of the tip insert, the ditch being configured and arranged toreceive the flexible electronic circuit.
 15. The ablation tip for theablation catheter of claim 9, wherein the conductive shell includes adomed distal end, a cylindrical body, and one or more isolatedtemperature-sensing islands, each of the temperature-sensing islands isconfined by a strip of insulative material, and configured to reducethermal transfer between the temperature-sensing islands and theconductive shell.
 16. An ablation catheter tip havinghigh-thermal-sensitivity, the tip comprising: a thermally-insulativeablation tip insert comprising a first portion and a second portion,wherein the insert is adapted to support at least one flexibleelectronic circuit including a plurality of temperature sensors; aconductive shell adapted to fit around the first portion of the insertin thermally-conductive contact with the plurality of temperaturesensors; and a shank adapted to cover the second portion of the insert,whereby the conductive shell and the shank are conductively coupled andtogether effectively encase the ablation tip insert.
 17. The ablationcatheter tip of claim 16, wherein the tip insert includes a ditch thatextends along an outer surface of the tip insert, the ditch beingconfigured and arranged to receive the flexible circuit.
 18. Theablation catheter tip of claim 16, wherein the conductive shell includesa domed distal end, a cylindrical body, and one or more isolatedtemperature-sensing islands, each of the temperature-sensing islands isconfined by a strip of insulative material, and configured to reducethermal transfer between the temperature-sensing islands and theconductive shell.
 19. The ablation catheter tip of claim 16, wherein thetip insert is constructed from a material selected from the groupconsisting of plastic and ceramic.